Stabilization of water sensitive clays

ABSTRACT

A method of treating a formation (e.g., subterranean), containing water sensitive clay minerals is provided. In this method, the formation is first treated with alcohol which will not appreciably swell or disperse the clay mineral. The formation is then contacted with phosphoric acid or phosphorous pentoxide, dispersed in a similar alcohol for a sufficient period of time to stabilize the clay mineral.

llnited States Patent [1 1 Thompson STABILIZATION OF WATER SENSITIVECLAYS Inventor: James L. Thompson, Tulsa, Okla.

Assignee: The Dow Chemical Company,

Midland, Mich.

Filed: Aug. 4, 1971 Appl. No.: 169,121

US. Cl. 166/305 R, 61/35 R Int. Cl E2lb 33/13 Field of Search 166/305 R;61/35 References Cited UNITED STATES PATENTS 11/1941 Bennett 166/305 RJune 12, 1973 3,444,931 5/1969 Braden, Jr 166/305 R PrimaryExaminer-Marvin A. Champion Assistant Examiner-Jack E. EbelAttorneyBruce M. Kanuch, Lloyd S. Jowanovitz [57] ABSTRACT 7 Claims, No-Drawings BACKGROUND OF THE INVENTION Many techniques have been devisedfor stabilizing water-sensitive formations containing clay minerals. Ingeneral, it may be desired to either increase the load bearing capacityof a formation and/or to maintain a certain degree of permeabilitytherein. Inthe former, it is not always necessary that the formationretain its permeability and thus certain chemical stabilizers dispersedin an aqueous medium can be employed. For example, it is taught byMichaels, Williams and Randolph, Industrial and Engineering Chemistry,Acidic Phosphorous Compounds as Soil Stabilizers, Vol. 50, No. 6, pp889-893, that an aqueous solution of phosphoric acid can be employed tosolidify and increase the load bearing capacity of clayey soils. In thismethod, the clay particles are actually cemented together. The abovemethod, however, cannot be employed to stabilize clayey formations whereit is desired to maintain a high degree of permeability, e.g., in oiland gas wells. Several methods have been discovered for permeabilitystabilizing some clayey soils. However, known techniques are notsuccessful on all types of clayey formations.

The present method can be employed to permeably stabilize (preventdispersing or swelling) certain clayey soils which are highly sensitiveto aqueous based stabilizing chemicals.

DESCRIPTION OF THE INVENTION A formation containing water sensitive clayminerals is first contacted with a sufficient quantity of an alcoholwhich will not appreciably disperse or swell the particular clayminerals in the formation, to remove aqueous based fluids from an areawhich is to be stabilized. Following this the same area is contactedwith a similar alcohol having dispersed therein phosphoric acid orphosphorous pentoxide. The formation is allowed to soak for a period oftime and the alcohol mixture is then removed with anoverflush of, forexample, water, brine or the like.

Specific alcohols which have been found to be useful in a formationcontaining one or more clay minerals, e.g., kaolinite, illite,montmorillonite, feldspar and/or chlorites, is methyl, ethyl alcohol ora mixture thereof. On the other hand, unexplainably isopropyl alcoholcaused the clay in the formation to be dispersed.

The phosphoric acid or phosphorous pentoxide is employed in methyl orethyl alcohol or mixture thereof in an amount ranging from about 2 toper cent by weight, preferably 4 to 6 per cent by weight of the alcoholcarrier.

The formation is flushed with from about 120 to 250 gallons of alcoholper foot of formation to be treated and soaked with about an equivalentamount of the alcohol dispersion.

The alcohol dispersion of phosphoric acid or phosphorous pentoxide isallowed to remain in contact with the formation for a sufficient periodof time to permeably stabilize the clay minerals in the formation. Thesoaking time will depend on such factors as the amount of constituentsin the formation, formation temperature strength of alcohol dispersionand the like.

The alcohol or mixture which is most efficacious on any particularformation containing water sensitive clay mineral and the optimumsoaking period can be readily determined by running simple laboratorytests on sample cores taken from the formation to be treated.Illustrative of such tests are those described in the followingexamples.

EXAMPLE 1 Certain oil wells located in Louisiana pass through a Mioceneformation S zone. The zone was causing considerable difficulty since itwas damaged, i.e., clay minerals were dispersed or swelled, by its ownproduced fluids. The zone could not be stabilized with zirconiumoxychloride, a known clay swelling control agent (U. S. Pat. No.3,382,924). X-Ray diffraction analysis of sample cores showed theformation to contain a major proportion of quartz and a minor proportion(less than 15 per cent) of a mixture of kaolinite, illite,montmorillonite, feldspar and chlorite minerals.

The following tests were run on frozen core samples taken from theformation.

For these tests, 1 inch O.-D. X 1% inch long core plugs were used. Thecore plugs were drilled from a frozen S sand core using liquid nitrogen.The frozen core plugs were placed in a core holder with a Hassler sleevepressure of 500 psi and the temperature of the core was increased toabout F, the temperature of the reservoir from which it was taken.Permeability measurements were obtained by metering certain fluidsthrough the core at a constant flow rate for volumetric measurements atthe outlet of the core and the pressure differential across the core wasmeasured with a Wiancho pressure transducer and indicator. Certainfluids were passed through the core at the reservoir temperature in thesequence indicated below in Table I.

TABLE I Core Fluid Permeability (md) l Kerosene 166 Isopropanol 136Formation Brine 49 2 Kerosene I45 Isopropanol 79 Formation Brine 29 3Kerosene I49 Isopropanol 42 Formation Brine 6l Kerosene was used toestablish the permeability of the core to an inert, non-damaging fluid.Isopropanol is miscible with the core test fluid and essentiallycomplete displacement of the core test fluid was obtained. Isopropanolis also miscible with the formation brine and was essentially displacedby that fluid. This permitted the measurement of the specificpermeability of the core with each test fluid and the data showed theeffect of each fluid on the permeability of the core. These data showthat the S sand was damaged by the injection of the formation brine.Also, these data indicated isopropanol caused formation damage.

Formation damage with isopropanol is rather unusual because it isgenerally considered to be an inert fluid to reservoir rock systems.Additional tests were performed to confirm the fluid flow data obtainedwith isopropanol. The test procedure consisted of adding five grams ofsand core material into a 25 ml graduated cylinder containing a certainfluid. The cylinder was stoppered and shaken until sand was evenlysuspended. The

system was allowed to stand quiescent for one hour.

Then the volume of settled solids was measured and a description of thedispersion of solids in the test fluids was recorded. The samemeasurements and observa- Therefore, these data suggested that the fourchemical tions were obtained after the system was allowed to solutionslisted above should not cause formation damstand quiescent for 24 hours.The test fluids used in age during a fluid flow test. these tests weredistilled water, formation brine, kero- The second step in the chemicalsolution reaction sene, and isopropanol. Distilled water was used inthese test was to remove the chemical solution from the gradtests toprovide a reference fluid which would caus uated cylinder and add ml offormation brine. The formation damagev The following data was obt in dgraduated cylinder was stoppered and shaken until the with these tests.sand particles were evenly suspended. The system was we. W TABLEH. W..

Results after one hour Results after 24 hours settling settling Originalvolume Volume Volume Descrip- Sample 'of dry of solid, Description ofsolid, tion of Number Test fluid sand, ml. ml. of dispersion inl. liquid1 Distilled water 3.3 Heavy 7.0 Milky. 2. Formation water 3.2 4.4 Medium4.1 Clear. 3... Kerosene 3.3 3.8 Clear 4.0 Do. 4 Isopropanol 3.3 3.8Light 4.0 Do.

1 Not settled.

The data indicate that the formation brine and isoallowed to standquiescent for 2 hours before the readpropanol react with particles inthe sand. However, the 20 ing and observations were taken. The followingresults reaction was considerably less with these fluids than wereObtained: with the distilled water. The amount of particles dis- TABLEIV persed in the various fluids after one hour of settling suggests thatthe following fluids would cause forma- Chemical Sol tion Removed and 5"Sand was Agitated with non damage and the amount of damage caused by theFormation Brine and Allowed fluids would decrease in the order as theyare listed: (1) I to Settle for Two Hours distilled water; (2) formationbrine; and (3) isopropag no]. The data also indicate that KCTOSGUC wouldbe an Sample Chemical Volume of Description Layer i t fl id f th dNumber Solution Solid ml of Liquid on Sand Th d d l f Treatment f testswere eslgne y Seml- 1 Formation brine 4.5 Slightly Yes quantitativelyexamination of the reaction of the fluids 2 g 4 0 gil Y with the 3"sand; however, the data appear to agree j, {313 i y 65 with theformation sensitivity data generated in the first zglconcilum oxyt C On8 part tTable I) of Example 1. The fluid flow and fluid 3 Methanol with5% 4'5 Milky Yes reaction data indicate that the sand contained waterbyvolume of zirconium oxychloride sensitive particles and that isopropanolshould not be 4 Methanol with 5% 4] Clear NO used as a solvent for anypreflush and afterflush treattime. t 5 Methanol with l0% 4.4 Clear No Hm. EXAMPLE 2 6 lrlqrljgiiainol with 2% 7.3 Clear Yes 7 D" In thisexample, a test procedure was used to screen 5351x 132; of 7 3 Clearchemical solutions for their ability to minimize or preurtyl ther f I lI et ylene glycol vent formation damage with the formation brine. The 8lsnpmpyl mom) 44 Clear YES first step of the test procedure was the sameas used in with 20% NHpH the dispersion and settling tests usingdistilled water, kerosene, isopropanol, and formation brine set forth inThese data indicate that methanol with 2 per cent Example I. Thefollowing results were obtained with NaOH should not be used in achemical treatment of the chemical solution treatments: the sand. Thedata also indicate that methanol with TABLETIII M Results after one hourResults after 24 hours Original settling 1 volume of dry Volume noSample SHsand, oisolid, Description of [)(BSiJ'lpLlUllnf number Chemicalsolution treatment nil. ml. dispersion liquid 1 Formation brine with 3%KCl 3.2 4. 4 Medium light 4. 4 Clear. 2 Formation brine with 5% byvolume of zirconium oxyeliloridn 3.2 4. 0 M dl [)o. 3 Methanol with 5%by volume of zirconium oxychlori lo 3. 4 4. 2 Light yellow. 4 Methanolwith 5% H3130: 3. 3 4. 2 Clear. 5. Methanol with 10% HiPoi an 4.0 Do,(Lu Methanol with 2% NaOlI c 4.0 4.4 Do. 7. Diesel #1 with 10% by volumeof bpItylether of ethylene glycol. 414) Do. 4. De.

8 Isopropylaleoholwith20% NII4O The dispersion data obtained for 1 hoursettling time per cent and l0 per cent H PO diesel No. l with butyl withthe various chemical solutions indicate that mcthether of ethyleneglycol and methanol with zirconium anol with 5 per cent and l0 per centH PO diesel with oxychloride treating fluids might be good stabilizing[0 per cent by volume of butyl ether of ethylene glycol chemicals forthe sand.

and isopropyl alcohol with 20 per cent by volume of NH OH resulted inthe smallest amount of dispersion. The description of the variouschemical solutions after EXAMPLE 3 24 hours settling time was about thesame. The volumes The experimental procedure used in these tests was ofthe settled solid particles were somewhat similar. the same as given inthe first test procedure described in Example 1. The fluids passedthrough the core in the sequence indicated.

Other chemical solutions were tested including 15 per cent HClcontaining 5 per cent and per cent by volume of zirconium oxychloride,diesel No. 1 with several surfactants, glacial acetic acid, alcohol with20 per cent by volume of NH OH, methanol with a combination of 5 percent H PO and 2 per cent by volume of oxtylamine, formation brine with 5per cent by volume of zirconium oxychloride, and formation brine with 3per cent KCl. The data from these latter fluid flow tests showed thatthese solutions were not effective as a clay stabilizing chemical forthe S sand.

Additional tests were then performed to further evaluate methanol with 5per cent H PO as a stabilizing agent. The experimental procedure waschanged so that the core system was allowed to stand at least 20 hoursafter the methanol-5 per cent H PO treatment and then the formationbrine permeability test was performed. The following results wereobtained:

TABLE VI Fluid Permeability (md) Test 1 Methanol 35 Methanol with 5% HPO 45 (Then core was allowed to stand 20 hours under pressure and atreservoir temperature) Formation Brine 49 Test 2 Methanol l 18 Methanolwith 5% H PO 140 (Standing 20 hours) Fonnation Brine 286 These data showthat a methanol with 5 per cent H PO chemical injection and 20 hours ofcure time will stabilize the sand for formation brine injection. Anothertest was performed using 10 per cent l-l PO and the results confirmedthe data obtained in Tests 1 and 2, Table VI. Therefore, additionaltests were performed to evaluate the methanol with 5 per cent H POtreatment for a simulated workover operation.

A series of fluid flow tests were performed to evaluate the methanol-HPO. treatment followed by a workover operation. The additional fluidflow tests after the 6 methanol-H PO treatment were: 9.6 lb/gal NaClsolution, 15 per cent HCl and a reverse flow test of the formationbrine. The following results were obtained:

TABLE VI] Fluid Permeability (md) Test 1 Methanol I44 Methanol with 5% HPQ, 91 (Standing 20 hours) Formation Brine 78 9.6 lb/gal NaCl Solution92 15% FIG! 86 Reverse flow of formation brine 74 Test 2 Methanol 66Methanol with 5% H PO 72 (Standing 20 hours) Formation Brine 154 9.6lb/gal NaCl Solution 1 10 15% HCl Reverse flow of formation brine 89These data indicate that the preflush of the methanol, the chemicaltreatment of methanol with 5 per cent H PO and a 20 hour cure time wassuccessful in stabilizing the sand for a subsequent workover operationand re-establis hing the previous production rates.

Similarly, treatments with phosphoric acid or phosphorous pentoxidedispersed in an alcohol, e.g., ethyl alcohol, which will not appreciablyswell or disperse certain clayey soils and sands is successful.

What is claimed is:

1. A method of permeably stabilizing a formation containing watersensitive clay minerals which comprises:

a. contacting the area of the formation to be stabilized with asufficient amount of an alcohol, which will not appreciably swell ordisperse said clay minerals, to remove a substantial amount of watercontained therein; and

b. following said contact with said alcohol, soaking said formation withan alcohol solution of phosphoric acid, said alcohol being one whichwill not swell or disperse said clay minerals.

2. The method of claim 1 wherein the first and secand alcohols are atleast one of methyl or ethyl alcohol.

3. The method of claim 1 wherein the area to be stabilizing is contactedand soaked with from about to 250 gallons of alcohol and alcoholsolution per foot of formation to be stabilized.

4. The method of claim 1 wherein the contacting alcohol and soakingalcohol is methyl alcohol.

5. The method of claim 4 wherein the formation is subterranean andlocated adjacent to a wellbore.

6. The method of claim 1 including in addition the step of removingspent alcohol solution of phosphoric acid from the formation.

7. The method of claim 1 wherein the formation is subterranean andlocated adjacent to a wellbore.

sm'ms PATENT OFCE" g Ti Q'EEQATE F Patent No. 3,738,425 Dated June 12,1973 lnv mcfl James L. Thompsdn It is certified that error appears inthe above-identified patent and that said Letters Patent are herebycorrected as shownbelow:

Column 4, Table IV, Sample No.7, column 2, delefe "1T 1" and insert l-.1 7

Column 4, Table IV, Sample No. 7, column 3, delete "7.3" and insert-5.,8--.

Signed and sealed this 12th day of March 19m.-

( SEAL)- Attest:

EDWARD MJLETCHER, JR. 1 Co MARSHALL" DANN Attesting Officer ICommissioner of Patents

2. The method of claim 1 wherein the first and second alcohols are atleast one of methyl or ethyl alcohol.
 3. The method of claim 1 whereinthe area to be stabilizing is contacted and soaked with from about 120to 250 gallons of alcohol and alcohol solution per foot of formation tobe stabilized.
 4. The method of claim 1 wherein the contacting alcoholand soaking alcohol is methyl alcohol.
 5. The method of claim 4 whereinthe formation is subterranean and located adjacent to a wellbore.
 6. Themethod of claim 1 including in addition the step of removing spentalcohol solution of phosphoric acid from the formation.
 7. The method ofclaim 1 wherein the formation is subterranean and located adjacent to awellbore.